Ink drop writing apparatus



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ALF/8E0 h. VCR/V 4. Film 5 W United States Patent 3,465,350 INK DROP WRITING APPARATUS Robert I. Keur, Niles, and Alfred H. Vorne, Chicago, Ill.,

assignors to A. B. Dick Company, Chicago, Ill., a corporation of Illinois Filed Mar. 13, 1968, Ser. No. 712,800 Int. Cl. G0ld 15/18 U.S. Cl. 346-75 6 Claims ABSTRACT OF THE DISCLOSURE In an apparatus of the type wherein ink under pressure is applied to a nozzle which is vibrated, and the ink emitted by the nozzle thereafter breaks down into ink drops which are charged in a charging tunnel in response to a video signal, means are provided, in accordance with this invention, for controlling the phase of the vibration of the nozzle relative to the video charging signal to insure correct phasing of the ink drops emitted by the nozzle and as a result proper charging of the ink drops by the video signal is made to occur. Properly charged ink drops will strike a detector, while improperly charged ink drops are deflected away from the detector.

BACKGROUND OF THE INVENTION An ink drop writing apparatus has been developed wherein ink is applied under pressure to a nozzle. The nozzle is vibrated in response to a synchronizing signal which is also used for synchronizing video signals. The vibrated nozzle causes an ink jet, which is emitted therefrom, to break up into uniform drops at a distance away from the tip of the nozzle. The rate of such drop formation is determined by the vibration rate. A means for charging each drop is provided at the location at which the ink stream begins to break into drops. This means usually is a conductive tube or cylinder. Video signals are applied between the nozzle and the cylinder in response to which a drop assumes a change determined by the ampli tude of the video signal at the time that the drop breaks away from the jet stream.

The drop thereafter passes through a fixed electric field, as a result of which it is deflected by an amount determined by the amplitude of the charge on the drop. At the boundary of the electric field there is positioned a writing medium upon which the drop falls. Since the deflection of the drop is determined by the charge on the drop, the arrangement enables one to write information with the ink which is carried by the video signal.

As previously stated, at the time that a drop separates from the fluid stream, the drops are charged by electrostatic induction. If the field established by the video signal is maintained while the drop separates, the drop will carry a change determined by this video signal. Obviously, if the video signal is in the process of rising or falling or is not present at the time the drops separate, the charge on the drop will not be that of the video signal. In order to place specific charges on given drops, one must know when drop separation is occurring or the phasing of the drop formation relative to the video signal. In the ab sence of control over drop separation time, because of unpredictable phase changes in the ink drop formation, the uniformity and the fidelity of the printing are affected adversely.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is to enable detection and correction of incorrect ink drop phasing.

It is another object of this invention to afford an arrangement for improving the uniformity and the fidelity of printing using an ink drop printing system.

Patented Sept. 2, 1969 Still another object of the present invention is the provision of apparatus which eliminates the problems created by incorrect time of drop formation.

This invention comprises an arrangement for providing test video signals for charging ink drops and detecting whether the ink drops are properly charged by placing an ink drop detector at the location to which they should be deflected if properly charged. If the ink drop detector does not detect ink drops, the phase of the formation of the ink drops is shifted to correct for this.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a block schematic drawing of a prior art ink drop writing system.

FIGURE 2 is a schematic drawing of an arrangement of an ink drop printing system with which this invention may be employed.

FIGURE 3 is an enlarged view illustrating ink drop formation in an ink drop printing system of this type.

FIGURE 4 is a schematic drawing of an ink drop phase correcting circuit in accordance with this invention, and

FIGURE 5 illustrates the modifications in ink drop apparatus of the type shown in FIGURE 1, which are required to be made with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGURE 1 is a schematic drawing of the presently known arrangement which is shown to afford a better understanding of the invention. An ink reservoir 10 provides ink under pressure to tubing 12 which is flexible. An electromechanical transducer 14 is usually placed adjacent to or around the tubing. The transducer is driven in response to signals from a source 16. The transducer serves to vibrate and/or compress the tubing 12 in the region of the nozzle 18. This results in an ink jet 20 being emitted which at a short distance downstream breaks up into drops 22 which are formed at a rate determined by the frequency of the vibration. In the region where the stream 20 breaks down into drops, a charging tunnel 24 is provided. This comprises a conductive cylinder to which video signals from a video signal source 26 are applied. The video signals establish a field within the charging tunnel so that the ink drops which are formed therein assume a charge determined by the amplitude of the video signal present at the time the drop separates from the ink jet 20.

Downstream of the charging tunnel there are usually placed a pair of electrodes 28 which are connected to' a field bias source 30. As a result, there is established between the electrodes a constant electric field. The ink drops, which bear charges in accordance with the video signal, enter this field and are deflected by an amount which is proportional to the amplitude of the charge. This enables intelligent writing to occur on a writing medium 32, which is moved at some synchronous rate past the electrodes. Drops which do not bear a video charge are captured by a tube or trough 34 which is judiciously placed at one side so as to capture these drops. It leads to a waste reservoir 36. The paper 32 moves into the plane of the drawing whereby its motion, together with the deflection of the drops, may be used for forming intelligible characters.

In order to write lines of information across a wide sheet of paper, an arrangement, such as is schematically represented in FIGURE 2, may be employed. Here, the ink drop writer 40 is attached to a traveling nut 42 which is geared to move on a journally supported lead screw 44.

At the top of the ink drop writer is a nut 46 which is free to slide along a rod 48. Accordingly, as the lead screw 44 is rotated in one direction or the other, the ink drop writer will move in a direction dictated by this rotation along a path parallel to the lead screw.

By ink drop writer is meant a housing which supports the ink reservoir 10, tubing 12, transducer 14, nozzle 20, and charging tunnel 24. The video and sync signal sources are placed elsewhere and are connected to the ink drop writer by wires. The function of the deflection electrodes 28 is preformed by a pair of spaced plates 41 which extend along the path of travel of the ink drop writer and are placed so that the stream of drops pass therethrough on their way to the paper. A trough (not shown) identical to the tube 34 is provided which extends adjacent the bottom plate.

The paper 50 upon which Writing is to occur moves in a direction vertical to the direction of the path of motion of the ink drop writer. A motor 52 has a first shaft 54 extending therefrom to a /2 sector gear 56. The motor has a second shaft 58 extending therefrom to a gear box 60, which functions to reverse the direction of rotation of the shaft 58. This reverse motion is communicated through a shaft 62 to another /2 sector gear 64 in which it terminates. The sector gears are cut so that as the motor rotates the sector gear 56 engages a gear 66 attached to one end of the lead screw to rotate the lead screw 44 so that the ink drop writer is moved from left to right. When the ink drop writer reaches the right hand end of the lead screw, the sector gear 56 is disengaged from the gear 66 and the sector gear 64 engages a gear 68 on the other end of the lead screw. This results in the lead screw being rotated in the opposite direction thereby returning the ink drop writer 40 to its home position on the left-hand side of the lead screw. Motor control apparatus 70' serves the function of energizing the motor to rotate over the interval required for the ink drop writer to make one round trip path along the lead screw. The motor control then waits until it receives a signal fro-m a gate, shown in FIGURE 4, which enables the motor to again function to cause the ink drop writer to make a round trip path.

A sensing switch circuit 72 has a feeler '74 which trips the sensing switch circuit when the ink drop writer returns to the home position. The sensing switch circuit may be any well known arrangement for generating a signal when the feeler 74 is actuated. This can be, for example, an arrangement for connecting a battery to the terminal 71 until the feeler 74 is out of contact with the ink drop writer.

FIGURE 3 is a view showing the ink drop writer at the home position with the housing partially removed to show the ink jet passing through the charging tunnel 14, which is broken away to enable one to view what is occurring therein. The ink jet which is emitted from the vibrated nozzle 18 begins to break down into drops 22 at a rate and at a phase determined by the phase and frequency of the sync signal source, within the charging tunnel. In accordance with this invention, and as will become more clear with the explanation of FIG- URE 4, a video signal at a predetermined frequency is used to charge the ink drops during an interval when the ink drop writer is in the home position, in order to determine whether or not the drops will be formed in phase with the video signals, which will be subsequently applied to the charging tunnel. If the drops are formed so that they will be in phase with the subsequently applied video signals, then they are deflected by the field between the electrodes 41 to a suitable drop detecting device 76. This can be a piece of piezoelectric material, 76 for example. The pz material generates pulse signals in response to the pressure of the successive drops falling thereon which is applied to an amplifier 78, for amplification. If the drops are not formed in phase with the applied signals, they will not receive a charge or charge of suf- 4.- ficient amplitude and thus will not strike the detector 78.

The circuitry for insuring the proper phasing of the formation of the ink drops is shown in block diagram form in FIGURE 4. The sensing switch 72 applies its output to a delay circuit 80 and also serves as the enabling input to an AND gate 86. The AND gate can then pass pulses which are received as the output of a flip-flop 82. A suitable frequency for these pulses may be 33 kHz., for example. The flip-flo is driven between its set and reset state in response to successive signals from a 66 kHz. signal source 80, which exemplifies the sync signal source for the nozzle transducer and for the video signal source. The output of the 66 kHz. signal source is also applied to a delay circuit which provides /2 of a 66 kc. pulse width delay. The outputs of the delay circuit 90 and of the AND gate 86 are applied to a second AND gate 92. The delay of the 66 kc. pulses results in AND gate 92 narrowing the 33 kc. interval allotted to the video pulses which are to be applied to the charging tunnel. The output of the AND gate 92 is applied to the charging tunnel 24. The purpose in narrowing the 33 kHz. pulses is to insure that a drop receives the full charge of the video pulse and not a charge from the rising front end or falling trailing edge of a video pulse. The arrangement for narrowing the 33 kHz. pulses is exemplary only. Any of the other well known techniques for pulse narrowing may be used.

If a drop is formed with the proper phasing, it receives the full charge of the 33 kc. pulse and will be deflected in passing through the constant electric field onto the drop detector 76. As previously indicated, the drop detector 76 drives an amplifier 78, whose output is applied to an integrator 94. The output of the integrator is applied to an inverter 96 and also to an AND gate 98, which also receives the output of the delay circuit 80. Should the drop detector be actuated in response to the drops, it is then known that the drops are being formed with the proper phase to receive the full charge of the video signals. This further indicates that the phase of the sync signal used for driving the transducer which vibrates the nozzle is proper and should not be altered. Under such a circumstance, the output of the integrator 94 which is now present is applied to an inverter 96 which inhibits the operation of an AND gate 100. The output of the integrator also is used to enable the AND gate 98 to pass the signal being received from the delay circuit 80 to the motor control circuit 70 (in FIGURE 1) whereby it can commence to drive the lead screw which moves the ink jet writer. The delay circuit 80 delays the signal received from the sensing switch long enough to enable the integrator 94 to accumulate the results of several rather than a sporadic drop.

Should drop detector 76 not provide an output signal, indicative of the fact that the phasing of the drops being formed is incorrect, then the output of the delay circuit 80 is applied as a first input to the AND gate 100. The signals from a clock signal source 102 serve as a second input to the AND gate 100. Upon the occurrence of the clock signal, a flip-flop 104 is driven to the state opposite to the one which it has at the time the output from the AND gate is received.

One of the outputs of the flip-flop 104 enables an AND gate 108, the other output of the flip-flop 104 enables an AND gate 106. 66 kc. signals from the source 84 are applied directly to AND gate 106 and through a 180 phase shift circuit 110 to the AND gate 108. As a result, an OR gate 112 receives the output of whichever one of the AND gates 106 or 108 has been enabled. Thus, the OR gate 112 output is 66 kc. in one phase or phase shifted therefrom. If the phase shifted 66 kc. signal corrects the phase of formation of the ink drops, then the drop detector 76 will be activated. Accordingly, integrator 94 output can then enable AND gate 98 to energize the motor control circuit. The ink drop apparatus will then make a round trip and when it reaches the home position the phase of the formation of the ink drops will be checked again.

FIGURE 5 shows the modification of the circuit arrangement shown in FIGURE 1, which is required in accordance with this invention. OR gate 112 is connected to drive the transducer 14 with its output. The charging tunnel is driven from the video signal source which receives its sync signals from the 66 kc. signal source. In addition, the charging tunnel is driven by the output of AND gate 92. The timing of the testing of the phasing of the formation of ink drops is made to occur within the retrace interval of the video signals, and therefore there will be no interference between the 33 kHz. test pulses being applied to the charging tunnel 24 and signals from the video signal source 26. The 33 kHz. test pulses are only applied to the charging tunnel when it is in the home position.

It will be noted that the sync frequency applied to the electromotive transducer 14 is 66 kHz. and the test video signal applied to the charging tunnel is 33 kHz. This means that the drops are formed at 66 kHz. rate but only every other drop receives a charge. This is done in order that the uncharged drops should act as a guard to minimize the adverse effects that arise due to the electric field caused by a charged drop interacting with the electric field caused by an adjacent charged drop. This is done as good practice. The test of proper phase of formation, however, is a valid one, despite the fact that a test charge is placed on every other drop instead of on every drop. However, this should not be construed as a limitation upon the invention since the invention operates equally well to test proper phasing with drops formed at a 66 kHz. rate and video signals applied at a 66 kHz. rate. Thus, the frequencies specified herein should be construed as exemplary and not as limiting.

Also, while the drop detector is illustrated as a piezoelectric crystal, it will be appreciated that this is exemplary structure only. For example, a micro switch that is actuated under drop pressure or other sensing device may be used in conjunction with the deflecting field to sense the adequacy of the drop charging.

There has accordingly been shown and described herein a novel and useful arrangement for testing and correcting the phasing of the formation of ink drops relative to video signals which are used for charging these ink drops whereby an improved ink drop writing system is provided.

What is claimed is:

1. In an ink drop writing system of the type wherein ink under pressure is delivered to a nozzle and the nozzle is vibrated by a transducer driven in response to synchronizing signals, the nozzle emitting an ink jet which breaks into drops in synchronism with the vibration of the nozzle, a charging tunnel is positioned in the region at which the ink jet breaks down into drops;

signals from a video signal source, which is synchronized by the sync signals, are applied to the charging tunnel for charging a drop formed therein, in response to the applied video signal, said charged ink drops passing out from the charging tunnel and thereafter through a fixed electric field which is established by a pair of spaced electrodes, said ink drops being deflected by said field in accordance with the charge on said ink drops;

the improvement in the phase of formation of said ink drops relative to the occurrence of a video signal on said charging tunnel comprising means for applying a fixed frequency charging signal to said charging tunnel;

means positioned adjacent said electrodes for receiving only ink drops which are charged by said fixed frequency signal and producing an output signal indicative thereof; and

means responsive to the absence of an output from said means for receiving for shifting the phase of said synchronizing signals to shift the phase of formation of ink drops in said charging tunnel to be in phase with the application of one of said fixed frequency and phase signals to said charging tunnel.

2. Apparatus as recited in claim 1 wherein said means for receiving said charged drops comprises a piezoelectric transducer.

3. A system as recited in claim 2 wherein said means responsive to the absence of a signal at the output of said detector means for shifting the phase of the synchronizing signals applied to said transducer includes:

an integrator having its input connected to said detecting means;

a first and second AND gate;

means for applying synchronizing signals to one input of said first AND gate;

a phase inverter;

means for applying synchronizing signals to said phase inverter;

means for applying the output of the phase inverter to an input of said second AND gate;

means for applying the outputs of said first and second AND gates to said motion transducer; and

switch means responsive to a lack of output from said inverter for enabling said first AND gate if said second AND gate is enabled at time or said second AND gate of said first AND gate is enabled at the time.

4. Ink drop apparatus including:

a source of ink under pressure;

a nozzle connected to receive ink from said source and to emit a jet of ink;

an electromotive transducer attached to said nozzle;

a source of synchronizing signals;

means for applying signals from said source of synchronizing signals to said electromotive transducer to cause said electromotive transducer to vibrate said nozzle whereby the ink jet which is emitted breaks into drops having a phase determined by the phase to said synchronizing signals;

a charging tunnel positioned at the region at which said ink jet breaks down into drops;

a source of video signals synchronized by said synchronizing signal source;

means for applying said video signals to said charging tunnel whereby each drop which is formed within said charging tunnel receives a charge as determined by said video signal;

a pair of deflection electrodes positioned adjacent the side of said charging tunnel through which said drops exit;

means for applying a fixed bias to said deflection electrodes to establish an electric field through which said drops pass;

drop receiving means positioned adjacent the downstream side of said deflecting electrodes for only receiving drops having a predetermined charge thereon;

means for applying fixed frequency and phase signals to said charging tunnel for charging drops formed therein whereby drops having the proper phase relative to said phase of said signals are received by said drop detecting means and drops not formed with the proper phase within said charging tunnel are not received by said receiving means; and

means responsive to an output from said receiving means for altering the phase of the synchronizing signals applied to said electromotive transducer until the drop receiving means does receive drops.

5. Apparatus as recited in claim 4 wherein there is included:

means for reciprocally moving said nozzle and said ink drop charging means from a home position at which said detector is located along to an end position and then back to said home position;

means for sensing when said ink drop apparatus returns to said home position; and

means. for enabling the application of said fixed frequency and phase signal to said charging tunnel only during the interval within which said ink drop apparatus is at said home position.

6. Apparatus as recited in claim 4 wherein said ink drop receiving apparatus includes:

a piezoelectric crystal;

an integrator connected to said piezoelectric crystal;

a first and a second AND gate;

means for applying signals from said source of synchronizing signals to one input of said AND gate;

a phase inverter having its out-put connected to one input of said second AND gate;

means for applying signals from said source of synchronizing signals to said phase inverter;

flip-flop means having a first and second outputs respectively connected to said first and second AND gate inputs;

means responsive to said home position sensing means for driving said flip-flop means to produce a first output when a second output is being produced at References Cited UNITED STATES PATENTS 3,298,030 1/1967 Lewis et a1. 34675 3,369,252 2/1968 Adams 346--75 3,373,437 3/1968 Sweet et a1. 346-7S 3,404,221 10/1968 Loughren 178-5.2

RICHARD B. WILKINSON, Primary Examiner JOSEPH W. HARTARY, Assistant Examiner US. Cl. X.R. 

